Page 314 - Machinery Component Maintenance

296 Machinery Component Maintenance and Repair

3. Balance the rotor, following the standard procedure for the ma-
chine, by applying corrections in two planes other than test planes
or those used for the unbalance masses in a maximum of four runs
at the balancing speed selected for the U,,, Test.
4. In the case of horizontal machines, after performing the actions de-
scribed in l to 3, change the angular reference system of the ma-
chine by 60 or go", e.g., turn the end-drive shaft with respect to the
rotor, turn black and white markings, etc.
5. For horizontal or vertical two-plane machines, attach in each of the
two prepared test plancs a test mass equal to ten times the claimed
minimum achievable residual unbalance.
For example, if the IS0 proving rotor No. 5 weighing 110 lbs
(50,000 g) is used, the weight of each test mass is calculated as fol-
lows:
The claimed minimum achievable residual specific unbalance is,
say

1 emar = O.ooOo20 in.

The claimed minimum achievable residual unbalance per test plane,
Le., for half the rotor weight, is therefore:

= 0.5 g in.

The desired 10 U,, test mass per plane is therefore equivalent to:

10 U,, (per plane)
= 10 - 0.5 g in.
= 5 g in.

If the test mass is attached so that its center of gravity is at a radius
of four in. (effective test mass radius), the actual weight of each test
mass will be:

5 goin.
m= = 1.25g
4 in.